Tubular lamp internal coating apparatus



Aug. 10, 1954 A. J. WEBB TUBULAR LAMP INTERNAL COATING APPARATU Filed Oct. 6, 1956" lnveh tor e w lw J i .WM 8 w m Patented Aug. 10, 1954 TUBULAR LAMPINTERN'AL COATING APPARATUS Arthur John Webb,Wolverton, England, assignor to General Electric Company, a corporation of New York 7 Application October 6, 1950, Serial No. 18l3,821

Claims priority, application Great Britain 7 March 24, .1950

.L 4 Claims. (Cl. 11s--215) This invention relates generally to the manufacture of tubular discharge lamps, and more particularly to apparatus for providing a coating or layer on the internal surface of the envelopes of such lamps. a

In the manufacture of low pressuretubular electric discharge lamps, it is sometimes desired to form, on the inside of the tubular envelope, a conducting stripe for use in initiating the discharge through the lamp; This conducting stripe extends along the inner periphery of the envelope into the neighborhood of electrodes mounted at each'end of the envelope. A convenient way of forming such a stripe is to deposit, along the path to be made conducting, a paste containing conductive particles, e. g.,: of metal or carbon, the liquid constituents ofthe paste beingsubsequently removed, orthe paste solidified by heat, to leave an adherent conducting layer of the particles. 1

It is an object of the present invention tov provide new and improved apparatus for depositing a thin layer or coating on the internal surface of tubular discharge lamps.

Another object of the invention is to provide an apparatus for internally coating the envelopes of low pressure discharge lamps, which apparatus is readily adaptable to automatic machine operation.

Still more particularly, an object of the present invention is to provide means for depositing a paste containing conductive particles such as described above, withinthe interiorof the envelope of .a tubular discharge lamp.

According to the invention, a carriage provid ing a reservoir forpasty material to bedeposited on the inner wall of the lamp envelope or tube and having means for distributing the material, is moved. relatively to, and longitudinally within, the tube by means of a magnet mounted externally to it.

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For further objects and advantages, and for a means may take the form of wheels or rollers which are arranged to dip into the fluid or pasty coating material contained within the reservoir, and also to make contact with the inner surface of the envelope. By using rotating members as opposed to wiping members, there is no relative movement between the inner surface of the envelope and the periphery of the wheel or roller. Such an arrangement is highly advantageous where it is desired to form a conductive path or ribbon on the interior of an envelope which has been previously coated with a luminescent material, because the luminescent coating is not disturbed thereby. The attraction of the magnet for the carriage mounted within the tubular envelope is made to provide the necessary pressure between the wheel or roller and the inner surface of the envelope and, at the same time, brings about the relative movement between the carriage and the envelope. 7

In the preferred embodiment of the invention, the carriage is in the form of a reservoir of nonmagnetic material containing the pasty material to be deposited on the internal surface of the envelope for eventually constituting the conductive path. The wheels or rollers mounted on the reservoir are made of a magnetic material so that they are attracted or pulled toward the pole piece of a magnet mounted outside the envelope. The magnet is preferably in the form of an electromagnet so that it can be energized, when necessary, to maintain the carriage stationary and de-energized, When desired, to permit the insertion of the carriage in, and its removal from, the tube to be coated.

Referring to the drawings, I indicates a glass tube which is to form the envelope of a fluorescent lamp, the tube being provided with an internal coating 2 of luminescent material. The tube is supported at one end upon a drum 3 and is supported at the other end upon a movable carriage d'p'rovided'with a clip 5 which encircles the end of the tube.

Mounted externally of the tube is an electromagnet 6 having a pole piece 7 which extends into proximity with the outer periphery of the tube l. Within the tube is shown the carriage 8 providing a reservoir 9 containing pasty material to be applied to a path along the interior of the tube, the reservoir being in the form of a rectangular trough made of nonmagnetic ma-- terial, such as brass. Mounted in the longitudinal parallel walls of the reservoir are spindles supporting rollers It! made of magnetic material, such as steel. The rollers have a thickness determined by the width of the path to be made conducting on the inner wall of the tube and are arranged in tandem so as to ensure th formation of an adequate coating on the tub and also to provide a two-point suspension for the carriage. As shown in Fig. 2, the pole piece I of the magnet is made in the form of a narrow strip adapted to extend between and beyond the peripheries of the rollers Ill, thus to concentrate the magnetic flux of the magnet onto the rollers. The lower periphery of each of the rollers dips into the pasty material within the reservoir; and, as they rotate along the inner surface of the tube, the pasty material is carried. onto the inner surface thereof.

In operating the apparatus, the tube I is first. placed in position on the drum 3, with its remote.

end supported on the carriage 4, and. the carriage 8 is then introduced into the tubeand the magnet 6 energized; The flux of the magnet thus attracts the rollers l and holds the carriage suspended within th tube. The tube isthen moved with relation to the carriag and magnet to cause the desired path to be provided with the coating of pasty material from the reservoir 9. The tube may conveniently be moved by driving the drum 3 through a source ofpower such as an electric motor and suitable gearing. The thickness of the paste deposited can be varied within limits by varying the speed of motion ofthe tube t.

While the invention has been described with reference to one particular arrangement for depositing a fluidor' pasty material on the internalsurface of an envelope in order to provide a relatively narrow conductive. path, it will readily be understood that the use of the invention is not restricted thereto. Thus, it may be utilized to provide other types of coatings on the internal surface of the tubular envelope; and it may. be adaptedtoprovide a coating covering substantially the entire inter-nal surface by means of suitable brushes or wipers. The appended claims are therefore intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire tosecure by Letters Patent of the United States is:

1. Apparatus for longitudinally coating the internal surface of a tubular envelope, comprising a reservoir for coating material and adapted to be located within said envelope, magnetic means to be located outside said envelope for creating a magnetic fieldtherein; means for imparting a displacement to said envelope along its longitudinal axis with respect to said magnetic means, a magnetic portion in said reservoir for main taining it in said magnetic field and in constant spaced relationship to said magnetic means notwithstanding displacement of said envelope, and a coating disc rotatably'mounted' on said reservoir, said disc having its lower periphery disposed for dipping in said material, and its upper periphery disposed for bearing against said internal surface, thereby to transfer coating material from said reservoir to said surface.

2. Apparatus for providing a longitudinal strip of a coating material" on the internal surface of a tubular envelope, comprising a reservoir for coating material and adapted to be located with- 4 in said envelope, magnetic means to be located outside said envelope for directing a magnetic field downwardly therein, a. magnetic portion in said reservoir for supporting it, withinsaid magnetic field, a pair of discs mountedin tandem on said reservoir with their peripheral plane parallel to the axis of said envelope, said discs serving to position said reservoir within said envelope below saidmagnet by bearing upwardly against the internal surface of said envelope, said discs beinggarranged-to; have their lower portions dipping into'said coating material in order to leave a deposit thereon against that portion of said internal, surfaQfi gainst which their upper surfaces bear, and'means for imparting a displacement: to said envelope along its longitudinal axis.

3 Apparatus for depositing a longitudinal strip of a. coating material on the internal surface of a tubular glass envelope, comprising a container serving as a reservoir of fluid coating material and) adapted: to be located" within said envelope, a magnet te -be located externally above said envelope for directing: a magnetic field therein, a: pair of rollers. mounted in tandem Within said container with their peripheral edges ina vertical. plane parallel to the. longitudinal axis of said envelope, said rollers. being adapted tohave their: lower edges, dip" into. saidv coating material and to have their upper edges bear upwardly against said internal surface, whereby said rollers. serve; to deposit said material in their track and toposition said container below said magnet, a magnetic portion within said reservoir for maintaining it withinsaid magnetic fieldand' drawing it up against the internal surface of said envelope inthe direction of said magnet, and means for" imparting a displacement to said envelope relative. to said magnet for causing said rollers to:- rotate and deposit said. material.

4. Apparatus for depositing a longitufinal strip of a coating material on the. internal surface of a tubular envelope, comprising a container serving as a reservoir of. coating. material and adapted to be located within. said envelope, an electromagnet to be located. vertically externally above said envelope in a manner to direct its magnetic field therein, a pair of discs composed of a magnetic material mounted within said COD. tainer with their peripheral edges in. a vertical plane parallel to the longitudinal axis of said envelope,- said' discs serving to maintain said container in spaced relationship to said magnet by reason of the upward 'p-ull of said magnetic field upon them, said discs bearingagainst. th internal surface of said envelope immediately above them and serving to deposit coating material picked up by their lower edges against said sur face, andmeansfor imparting a displacement to said envelope rel'ativeto. said electromagnet, said displacement being along the longitudinal axis of said envelope.

References Cited in the are of this patent UNITED srarns PATENTS 

